The vehicle headlamps are controlled by the body control module (BCM) based on inputs from the headlamp switch and the turn signal/multifunction switch. The headlamp switch has four positions: Off, Auto, Park, and Headlamps. The default headlamp switch position is Auto, in which the BCM uses the ambient light sensor to determine when headlamps are needed. The Off portion of the headlamp switch is a momentary switch which overrides the automatic headlamps and will turn off the vehicle headlamps. When in the Off position, the headlamp switch grounds the headlamp switch headlamps off signal circuit, prompting the BCM to turn off the headlamps. The Park position of the headlamp switch will only illuminate the vehicle parking lamps. The Headlamp position of the headlamp switch will illuminate both the parking lamps, as well has the headlamps. With the headlamp switch in the Headlamp position, the headlamp switch headlamps on signal circuit is grounded, prompting the BCM to turn on the headlamps, regardless of other factors such as ambient light.

The headlamp high beams are controlled through the flash to pass switch and the headlamp dimmer switch, both located in the turn signal/multifunction switch. The flash to pass switch is a momentary type switch, designed to illuminate the high beams as long as the switch is held. With the switch closed, the flash to pass switch signal circuit is grounded, prompting the BCM to turn on the high beam lamps. The headlamp dimmer switch allows the operator to select between full time high or low beam operation. Unlike the flash to pass switch, it is not a momentary switch. When the headlamp dimmer switch is in the high beam position, the headlamp dimmer switch high beam signal circuit is grounded. This prompts the BCM to turn on the high beam lamps.

The BCM controls the headlamps based on the inputs explained above. When a low beam request is received, the BCM grounds the headlamp low beam relay control circuit. This energizes the coil in the HID/LO BEAM relay, causing the relay switch to close. This then applies B+ to both low beam headlamps through the LT LO BEAM and RT LO BEAM fuses, illuminating the low beam headlamps. When a high beam request is received, the BCM grounds the headlamp high beam relay control circuit. This energizes the coil in the HI BEAM relay, causing the relay switch to close. This then applies B+ to both high beam headlamps through the LT HI BEAM and RT HI BEAM fuses, illuminating the high beam headlamps.

Schematic Reference

Headlights/Daytime Running Lights (DRL) Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Exterior Lighting Systems Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, observe the scan tool Auto Hdlp. Disable Sw. parameter while cycling the headlamp switch between the Auto and Off positions. The parameter should cycle between Active and Inactive.

⇒	If the parameter does not cycle between the specified values, refer to Headlamp Switch Malfunction.

2. Observe the scan tool Headlamp Switch parameter while cycling the headlamp switch between the Auto and Head position. The parameter should cycle between Active and Inactive.

⇒	If the parameter does not cycle between the specified values, refer to Headlamp Switch Malfunction.

3. With the headlamps ON, observe the scan tool Flash to Pass Switch parameter while pulling and releasing the flash to pass switch. The parameter should cycle between Active and Inactive.

⇒	If the parameter does not cycle between the specified values, refer to Turn Signal/Multifunction Switch Malfunction.

4. With the headlamps ON, observe the scan tool High Beam Select Switch parameter while switching the headlamp dimmer switch between the low and high beam positions. The parameter should cycle between Active and Inactive.

⇒	If the parameter does not cycle between the specified values, refer to Turn Signal/Multifunction Switch Malfunction.

5. Command the Low Beams ON and OFF with a scan tool. Verify the low beam headlamps turn ON and OFF.

⇒	If the low beam headlamps do not cycle between the commanded states, refer to Low Beam Headlamp Malfunction.

6. Command the High Beams ON and OFF with a scan tool. Verify the low beam headlamps turn ON and OFF.

⇒	If the high beam headlamps do not cycle between the commanded states, refer to High Beam Headlamp Malfunction.

Headlamp Switch Malfunction

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Verify that a test lamp illuminates between the ground circuit terminal 8 and B+.

⇒	If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

3. Ignition ON, test for B+ between the signal circuit terminals listed below and ground.

•	Headlamp switch headlamps ON signal terminal 1

•	Park lamp switch ON signal terminal 2

•	Headlamp switch OFF signal terminal 3

⇒	If less than the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM.

4. Install a 3A fused jumper wire between the park lamp ON signal circuit terminal 2 and ground. Verify the scan tool Parklamp Switch parameter is Active.

⇒	If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

5. Install 3A fused jumper wires between both signal circuit terminals listed below and ground. Verify the scan tool Headlamp Switch parameter is Active.

•	Headlamp ON terminal 1

•	Park lamp signal terminal 2

⇒	If not the specified value, test the signal circuit terminal 1 for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

6. Remove the jumper wires from terminal 1 and terminal 2. Install a 3A fused jumper wire between the signal circuit terminal 3 and ground. Verify the scan tool Auto Hdlp. Disable Sw. parameter is Active.
7. If all circuits test normal, replace the headlamp switch.

Turn Signal/Multifunction Switch Malfunction

1. Ignition OFF, disconnect the (C2) harness connector at the turn signal/multifunction switch.
2. Ignition OFF, test for less than 5.0 ohms of resistance between the ground circuit terminal 8 and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify the scan tool Flash to Pass Switch parameter is Inactive.

⇒	If not the specified value, test the signal circuit terminal 10 for a short to ground. If the circuit tests normal, replace the BCM.

4. Verify the scan tool High Beam Select Switch parameter is Inactive.

⇒	If not the specified value, test the signal circuit terminal 7 for a short to ground. If the circuit tests normal, replace the BCM.

5. Install a 3A fused jumper wire between the signal circuit terminal 10 and ground. Verify the scan tool Flash to Pass Switch parameter is Active.

⇒	If not the specified value, test the signal circuit for a short to voltage or and open/high resistance. If the circuit tests normal, replace the BCM.

6. Install a 3A fused jumper wire between the signal circuit terminal 7 and ground. Verify the scan tool High Beam Select Switch parameter is Active.

⇒	If not the specified value, test the signal circuit for a short to voltage or and open/high resistance. If the circuit tests normal, replace the BCM.

7. If all circuits test normal, test or replace the turn signal/multifunction switch.

Low Beam Headlamp Malfunction - without RPO TSH/TVC/TVD

1. Ignition OFF, disconnect the HID/LO BEAM relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay controlled output circuit terminal 87 and ground.

⇒	If the test lamp illuminates, test the relay controlled output circuit for a short to voltage.

3. Verify that a test lamp illuminates between the relay coil B+ circuit terminal 85 and ground.

⇒

If the test lamp does not illuminate, test the relay coil B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay coil B+ circuit fuse is open, test the relay controlled output circuit for a short to ground. If the circuit tests normal, test or replace the HID/LO BEAM relay.

4. Verify that a test lamp illuminates between the relay switch B+ circuit terminal 30 and ground.

⇒	If the test lamp does not illuminate, test the relay switch B+ circuit for an open/high resistance.

5. Connect a test lamp between the relay coil B+ circuit terminal 85 and the relay coil control circuit terminal 86.
6. Command the low beam headlamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the relay coil control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

7. Connect a 20A fused jumper wire between the relay switch B+ circuit terminal 30 and the relay controlled output circuit terminal 87.
8. Disconnect the harness connector at one of the low beam headlamps.
9. Verify that a test lamp illuminates between the low beam headlamp control circuit listed below and ground:

•	RPO WDA - terminal B

•	RPO Z88 - terminal A

⇒	If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance.

10. Verify that a test lamp illuminates between the low beam headllamp ground circuit listed below and B+:

•	RPO WDA - terminal A

•	RPO Z88 - terminal B

⇒	If the test lamp does not illuminate, test the ground circuit for a open/high resistance.

11. If all circuits test normal, test or replace the HID/LO BEAM relay.

Low Beam Headlamp Malfunction - with RPO TSH/TVC/TVD

1. Ignition OFF, disconnect the HID/LO BEAM relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay controlled output circuit terminal 87 and ground.

⇒	If the test lamp illuminates, test the relay controlled output circuit for a short to voltage.

3. Verify that a test lamp illuminates between the relay coil B+ circuit terminal 85 and ground.

⇒

If the test lamp does not illuminate, test the relay coil B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay coil B+ circuit fuse is open, test the relay controlled output circuit for a short to ground. If the circuit tests normal, test or replace the HID/LO BEAM relay.

4. Verify that a test lamp illuminates between the relay switch B+ circuit terminal 30 and ground.

⇒	If the test lamp does not illuminate, test the relay switch B+ circuit for an open/high resistance.

5. Connect a test lamp between the relay coil B+ circuit terminal 85 and the relay coil control circuit terminal 86.
6. Command the low beam headlamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the relay coil control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

7. Connect a 20A fused jumper wire between the relay switch B+ circuit terminal 30 and the relay controlled output circuit terminal 87. The low beam headlamps should not illuminate.

⇒	If the low beam headlamps illuminate, test or replace the HID/LO BEAM relay.

8. With the jumper wire still connected, disconnect the harness connector at one of the low beam headlamps.
9. Verify that a test lamp illuminates between the low beam control circuit listed below and ground:

•	RPO WDA - terminal 5

•	without RPO WDA - terminal 7

⇒	If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance.

10. Verify that a test lamp illuminates between the low beam headllamp ground circuit terminal 6 and B+.

⇒	If the test lamp does not illuminate, test the ground circuit for a open/high resistance.

11. If all circuits test normal, test or replace the headlamp assembly.

High Beam Headlamp Malfunction - RPO TSH/TVC

1. Ignition OFF, disconnect the HI BEAM relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay controlled output circuit terminal 87 and ground.

⇒	If the test lamp illuminates, test the relay controlled output circuit for a short to voltage.

3. Verify that a test lamp illuminates between the relay coil B+ circuit terminal 85 and ground.

⇒

If the test lamp does not illuminate, test the relay coil B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay coil B+ circuit fuse is open, test the relay controlled output circuit for a short to ground. If the circuit tests normal, test or replace the HI BEAM relay.

4. Verify that a test lamp illuminates between the relay switch B+ circuit terminal 30 and ground.

⇒	If the test lamp does not illuminate, test the relay switch B+ circuit for an open/high resistance.

5. Connect a test lamp between the relay coil B+ circuit terminal 85 and the relay coil control circuit terminal 86.
6. Command the high beam headlamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the relay coil control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

7. Connect a 20A fused jumper wire between the relay switch B+ circuit terminal 30 and the relay controlled output circuit terminal 87. The high beam headlamps should not illuminate.

⇒	If the high beam headlamps illuminate, test or replace the HI BEAM relay.

8. With the jumper wire still connected, disconnect the harness connector at the appropriate headlamp high beam solenoid module.
9. Verify that a test lamp illuminates between the high beam headlamp control circuit terminal 5 and ground.

⇒	If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance.

10. Verify that a test lamp illuminates between the headlamp high beam solenoid module ground circuit terminal 4 and B+.

⇒	If the test lamp does not illuminate, test the ground circuit for a open/high resistance.

11. If all circuits test normal, test or replace the headlamp assembly.

High Beam Headlamp Malfunction - without RPO TVC/TVD

1. Ignition OFF, disconnect the HI BEAM relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay controlled output circuit terminal 87 and ground.

⇒	If the test lamp illuminates, test the relay controlled output circuit for a short to voltage.

3. Verify that a test lamp illuminates between the relay coil B+ circuit terminal 85 and ground.

⇒

If the test lamp does not illuminate, test the relay coil B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay coil B+ circuit fuse is open, test the relay controlled output circuit for a short to ground. If the circuit tests normal, test or replace the HI BEAM relay.

4. Verify that a test lamp illuminates between the relay switch B+ circuit terminal 30 and ground.

⇒	If the test lamp does not illuminate, test the relay switch B+ circuit for an open/high resistance.

5. Connect a test lamp between the relay coil B+ circuit terminal 85 and the relay coil control circuit terminal 86.
6. Command the high beam headlamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the relay coil control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

7. Connect a 20A fused jumper wire between the relay switch B+ circuit terminal 30 and the relay controlled output circuit terminal 87.
8. Disconnect the harness connector at one of the high beam headlamps.
9. Verify that a test lamp illuminates between the high beam headlamp control circuit listed below and ground:

•	RPO WDA - terminal B

•	RPO Z88 - terminal A

⇒	If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance.

10. Verify that a test lamp illuminates between the high beam headllamp ground circuit listed below and B+:

•	RPO WDA - terminal A

•	RPO Z88 - terminal B

⇒	If the test lamp does not illuminate, test the ground circuit for a open/high resistance.

11. If all circuits test normal, test or replace the HI BEAM relay.

High Beam Headlamp Malfunction - with RPO TVD

1. Ignition OFF, disconnect the HI BEAM relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay controlled output circuit terminal 87 and ground.

⇒	If the test lamp illuminates, test the relay controlled output circuit for a short to voltage.

3. Verify that a test lamp illuminates between the relay coil B+ circuit terminal 85 and ground.

⇒

If the test lamp does not illuminate, test the relay coil B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the relay coil B+ circuit fuse is open, test the relay controlled output circuit for a short to ground. If the circuit tests normal, test or replace the HI BEAM relay.

4. Verify that a test lamp illuminates between the relay switch B+ circuit terminal 30 and ground.

⇒	If the test lamp does not illuminate, test the relay switch B+ circuit for an open/high resistance.

5. Connect a test lamp between the relay coil B+ circuit terminal 85 and the relay coil control circuit terminal 86.
6. Command the high beam headlamps ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the BCM.

⇒	If the test lamp is always OFF, test the relay coil control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM.

7. Connect a 20A fused jumper wire between the relay switch B+ circuit terminal 30 and the relay controlled output circuit terminal 87. The high beam headlamps should not illuminate.

⇒	If the high beam headlamps illuminate, test or replace the HI BEAM relay.

8. With the jumper wire still connected, disconnect the harness connector at the appropriate headlamp high beam solenoid.
9. Verify that a test lamp illuminates between the high beam headlamp control circuit listed below and ground.

•	RPO W49 terminal 2

•	RPO WDA terminal 1

•	RPO Z88 terminal II

⇒	If the test lamp does not illuminate, test the control circuit for a short to ground or an open/high resistance.

10. Verify that a test lamp illuminates between the headlamp high beam solenoid ground circuit listed below and B+.

•	RPO W49 terminal 1

•	RPO WDA terminal 3

•	RPO Z88 terminal I

⇒	If the test lamp does not illuminate, test the ground circuit for a open/high resistance.

11. If all circuits test normal, test or replace the headlamp assembly.

Headlamp Switch

1. Ignition OFF, disconnect the harness connector at the headlamp switch.
2. Test for infinite resistance between the signal terminal 3 and the ground terminal 8 with the switch in the Auto position.

⇒	If not the specified value, replace the headlamp switch.

3. Test for infinite resistance between the signal terminal 1 and the ground terminal 8 with the switch in the Auto position.

⇒	If not the specified value, replace the headlamp switch.

4. Test for less than 2.0 ohms of resistance between the signal terminal 3 and the ground terminal 8 with the switch in the Off position.

⇒	If not the specified value, replace the headlamp switch.

5. Test for less than 2.0 ohms of resistance between the signal terminal 1 and the ground terminal 8 with the switch in the Headlamp position.

⇒	If not the specified value, replace the headlamp switch.

Turn Signal/Multifunction Switch

1. Ignition OFF, disconnect the harness connector C2 at the turn signal/multifunction switch.
2. Test for infinite resistance between the signal terminal 10 and the ground terminal 8 with the flash to pass switch in the open position.

⇒	If not the specified value, replace the turn signal/multifunction switch.

3. Test for infinite resistance between the signal terminal 7 and the ground terminal 8 with the headlamp dimmer switch in the low beam position.

⇒	If not the specified value, replace the turn signal/multifunction switch.

4. Test for less than 2.0 ohms of resistance between the signal terminal 10 and the ground terminal 8 with the flash to pass switch in the closed position.

⇒	If not the specified value, replace the turn signal/multifunction switch.

5. Test for less than 2.0 ohms of resistance between the signal terminal 7 and the ground terminal 8 with the headlamp dimmer switch in the high beam position.

⇒	If not the specified value, replace the turn signal/multifunction switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.